1. Field of the Invention
This invention relates generally to multi-chip module systems and their method of fabrication. More specifically, the present invention relates to multi-chip module systems and their method of fabrication using known-good-die (KGD) therein.
2. State of the Art
An integrated circuit (IC) typically includes a semiconductor die (die) electrically attached to a leadframe, which provides physical support for the die and is used to connect the die with external circuitry located on a substrate. In such an arrangement, the leadframe and die are typically connected by means of wires, such as gold, aluminum, etc., being encapsulated within a plastic package, although ceramic and metal packages may also be used depending on the operating environment and the packaging requirements of the die.
With ever increasing demands for miniaturization and higher operating speeds, multi-chip module systems (MCM's) are increasingly attractive in a variety of electronics. MCM's, which contain more than one die, can help minimize the system operational speed restrictions imposed by long printed circuit board connection traces by combining, for example, the processor, memory, and associated logic into a single package. In addition, MCM's offer packaging efficiency.
Generally, MCM's may be designed to include more than one type of die within a single package, or may include multiples of the same die, such as the single in-line memory module (SIMM) or single in-line package (SIP).
It is well known that semiconductor dies have an early failure rate, often referred to in reliability terms as infant mortality. As with all assemblies, this phenomenon is also present in MCM's. For example, an MCM composed of ten dice, each die having an individual reliability yield of 95%, would result in a first pass test yield of less than 60%, while an MCM composed of twenty dice, each die having an individual reliability yield of 95%, would produce a first pass test yield of less than 36%. The market's perception of this phenomenon affects the decision to use MCM's in various applications.
Previously, an unacceptable die in an MCM, which has been subjected to burn-in and testing, has required either the replacement of such a die or the discard of the MCM. Both being time consuming and expensive. Additionally, since replacing an unacceptable die on an MCM poses risks to other MCM components during the replacement operation, it may be desirable to discard an MCM with such a die, rather than attempt rework the MCM, particularly where the reliability of the replacement die is not known.
Depending on the extent of testing and/or burn-in procedures employed, a die may typically be classified into varying levels of reliability and quality. For example, a die may meet only minimal quality standards by undergoing standard probe testing or ground testing while still in wafer form, while an individual separated die may be subjected to tests at full-range temperatures with full burn-in being subsequently termed a known-good-die (KGD).
A cost-effective method for producing known reliable MCM's is desirable for industry acceptance and use of MCM's in various applications. In an attempt to provide known reliable MCM's complying with consumer requirements, it is desirable either to fabricate an MCM of KGD or to fabricate an MCM of probe tested dice and subsequently subject the MCM to burn-in and performance testing. However, using only KGD in an MCM may not be cost effective since each KGD has been subjected to performance and burn-in testing, which are costly. In contrast to the use of all KGD in an MCM, when using die with well known production and reliability histories, particularly where the die being used is known to have a low infant mortality rate, the use of such minimally tested die to produce an MCM may be the most cost effective alternative.
As previously stated, since typical testing and burn-in procedures are generally labor and time intensive posing significant risks to the dice of an MCM, in an instance where an MCM is produced from minimally tested die, in the event that MCM contains an unacceptable die, replacement of unacceptable die with a KGD is preferable in the rework of the MCM because rework with KGD should not require the MCM to be subjected to further burn-in, but rather, only performance testing.
An example of a multi-chip module having a plurality of dynamic random access memory devices (DRAM's) used as memory in a computer is illustrated in U.S. Pat. No. 4,992,850, issued Feb. 12, 1991, to Corbett et al., assigned to the assignee of the present invention.
An example of a method and apparatus for the testing and burn-in of an individual die prior to packaging is illustrated in U.S. Pat. No. 5,424,652, issued Jun. 13, 1995, to Hembree et al., assigned to the assignee of the present invention. Such a method and apparatus provide a source of KGD to allow for the rework of an unacceptable die in an MCM with a KGD.
Other examples of a method for the testing and burn-in of an individual die prior to packaging are illustrated in U.S. Pat. No. 5,448,165 and 5,475,317.
In other instances, it is known to test a die in a package for functionality and replace any defective die. Such is illustrated in U.S. Pat. Nos. 5,137,836, 5,378,981, and 5,468,655.
In yet another instance, as illustrated in U.S. Pat. No. 5,239,747 and 5,461,544, it is known to test a multi-chip module (SIMM) to determine if any of the semiconductor devices mounted thereon are non-functional and, if so, replace the defective device with a device which has either been subjected to burn-in, or the entire multi-chip module can be subjected to another burn-in process after the replacement of the defective device. However, the defective devices are merely replaced by removing the defective device and replacing it with another, either a device subjected to burn-in or not. This process can be complicated, time consuming and costly depending upon the type of device, the type of mounting of the device on the substrate, and the type of substrate used for mounting.
Therefore, a need exists for the cost-efficient fabrication of MCM's of known performance and reliability requirements.